NAME¶
glLogicOp - specify a logical pixel operation for rendering
C SPECIFICATION¶
void
glLogicOp(GLenum opcode);
PARAMETERS¶
opcode
Specifies a symbolic constant that selects a
logical operation. The following symbols are accepted: GL_CLEAR,
GL_SET, GL_COPY, GL_COPY_INVERTED, GL_NOOP,
GL_INVERT, GL_AND, GL_NAND, GL_OR, GL_NOR,
GL_XOR, GL_EQUIV, GL_AND_REVERSE, GL_AND_INVERTED,
GL_OR_REVERSE, and GL_OR_INVERTED. The initial value is
GL_COPY.
DESCRIPTION¶
glLogicOp specifies a logical operation that, when enabled, is applied
between the incoming RGBA color and the RGBA color at the corresponding
location in the frame buffer. To enable or disable the logical operation, call
glEnable() and
glDisable() using the symbolic constant
GL_COLOR_LOGIC_OP. The initial value is disabled.
Opcode |
Resulting Operation |
GL_CLEAR |
0 |
GL_SET |
1 |
GL_COPY |
s |
GL_COPY_INVERTED |
~s |
GL_NOOP |
d |
GL_INVERT |
~d |
GL_AND |
s & d |
GL_NAND |
~(s & d) |
GL_OR |
s | d |
GL_NOR |
~(s | d) |
GL_XOR |
s ^ d |
GL_EQUIV |
~(s ^ d) |
GL_AND_REVERSE |
s & ~d |
GL_AND_INVERTED |
~s & d |
GL_OR_REVERSE |
s | ~d |
GL_OR_INVERTED |
~s | d |
opcode is a symbolic constant chosen from the list above. In the
explanation of the logical operations,
s represents the incoming color
and
d represents the color in the frame buffer. Standard C-language
operators are used. As these bitwise operators suggest, the logical operation
is applied independently to each bit pair of the source and destination
colors.
NOTES¶
When more than one RGBA color buffer is enabled for drawing, logical operations
are performed separately for each enabled buffer, using for the destination
value the contents of that buffer (see
glDrawBuffer()).
Logic operations have no effect on floating point draw buffers. However, if
GL_COLOR_LOGIC_OP is enabled, blending is still disabled in this case.
ERRORS¶
GL_INVALID_ENUM is generated if
opcode is not an accepted value.
ASSOCIATED GETS¶
glGet() with argument
GL_LOGIC_OP_MODE.
glIsEnabled() with argument
GL_COLOR_LOGIC_OP.
SEE ALSO¶
glBlendFunc(),
glDrawBuffer(),
glEnable(),
glStencilOp()
COPYRIGHT¶
Copyright © 1991-2006 Silicon Graphics, Inc. This document is licensed
under the SGI Free Software B License. For details, see
http://oss.sgi.com/projects/FreeB/.